Conventionally, in this type of apparatus, the top board is made to perform a tilting motion by rotating the top board about the axis of the lateral direction of the top board (see, for example, Patent Documents 1 to 7). Note that Patent Document 2: Japanese Unexamined Patent Application Publication No. 2004-159815 is a Japanese patent family of Patent Document 7: U.S. Pat. No. 7,000,271. In this type of apparatus, when a subject (patient) laid on the top board is inclined by the tinting motion, the region of interest (ROI: Region of Interest) shifts, the distance (SOD: Source Object Distance) between the X-ray tube and the subject changes, and the X-ray passing angle changes. For this reason, it is required to automatically maintain the region of interest in accordance with the tilting motion as described in each Patent Document.